In the case of producing pure water used in the technical fields of washing parts in the electronic industry, the production of medicaments, etc., distilled water or pure water produced in a primary purification such as an ion exchange, etc., is used. Also used is water, the purity of which is improved by being supplied to a pure-water producing apparatus containing a polisher, etc. to further remove impurities such as particles, etc. Pure water thus produced is supplied to use point(s) through a supply line and, after it is used for washing, etc., any unused or used pure water is recycled to the foregoing primary purification step and reused.
Also, for improving the treatment efficiency of washing, etc., it has been attempted to dissolve ozone in pure water described above to form ozone-containing water and use the water for the treatment aforementioned such as washing parts, etc.
Since ozone has a stronger oxidizing power than chlorine, it has an effect for sterilization, deodorization, decolorization, etc., and is relatively easily decomposed into oxygen after the oxidizing action, whereby the problem of secondary pollution does not occur, the utilization of ozone is growing.
However, the decomposition of ozone in the above-described cases is insufficient, whereby a small amount of ozone remains, and oxygen, which is the decomposition product of ozone, is also dissolved in the water. For completely removing these remaining gases, at present, an active carbon treatment has been carried out, and the water thus treated is discharged in a river. In this case, if the water treated is circulated to the pure water circulating step described above, the treated water contains excessive impurities caused from the active carbon, and hence it is substantially impossible to use the treated water for the circulation step. Also, since the foregoing remaining gases have a bad influence on the pure-water producing apparatus, etc., it is inappropriate to circulate the water to the pure-water producing apparatus without applying a gas removal operation. For solving this problem, a method of using pipes composed of a material which is unsuitable for the growth of bacteria, and a method of carrying out the decomposition of ozone by a low-tension ultraviolet ozone decomposition apparatus directly before the foregoing pure-water producing apparatus (unexamined published Japanese patent application No. 2-144195), have been proposed. However, this method of carrying out ozone decomposition utilizing low-tension ultraviolet rays, has the disadvantage that the ozone in water is reluctant to decompose completely, and thus ozone is contained in the water being supplied to the pure-water producing apparatus, whereby the function of the pure-water producing apparatus becomes insufficient.